[atlas] Link-Local ICMP messages for Atlas probe

Hi,

On Thu, Aug 17, 2023 at 03:50:03PM -0700, Daryl Morse wrote:
> I used WireShark on the WAN interface and I can confirm that the messages
> are all ping requests. Further, I can confirm that all of the addresses have
> been mangled. They are logged as fe80:5::, but the correct addresses are
> fe80::. I created a bug report.

Now that might be an API artefact.  Some of the BSD based OSes report the
interface ID in bits 16..31 when returning a fe80:: address in a
sockaddr structure.

The usual code to deal with it does something like this... from OpenVPN's
"give me the current IPv6 default gateway via a routing socket query" code:

    /* get gateway addr and interface name */

        struct sockaddr_in6 *s6 = (struct sockaddr_in6 *)gate;
        struct in6_addr gw = s6->sin6_addr;

        /* You do not really want to know... from FreeBSD's route.c
         * (KAME encodes the 16 bit scope_id in s6_addr[2] + [3],
         * but for a correct link-local address these must be :0000: )
         */
        if (gate->sa_len == sizeof(struct sockaddr_in6)
            && IN6_IS_ADDR_LINKLOCAL(&gw) )
        {
            gw.s6_addr[2] = gw.s6_addr[3] = 0;
        }


Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

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